Challenge 2: Manage a Many-to-Many Relationship — Possible Solution
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use App\Models\Book;
use App\Models\Tag;

$book = Book::find(1);
$sciFiTag = Tag::firstOrCreate(['name' => 'sci-fi']);
$classicTag = Tag::firstOrCreate(['name' => 'classic']);
$favoriteTag = Tag::firstOrCreate(['name' => 'favorite']);

// 1. Attach two tags to the book
$book->tags()->attach([$sciFiTag->id, $classicTag->id]);
// $book->tags now contains: sci-fi, classic

// 2. Remove one of them
$book->tags()->detach($classicTag->id);
// $book->tags now contains: sci-fi

// 3. Replace the ENTIRE tag list with sync()
$book->tags()->sync([$sciFiTag->id, $favoriteTag->id]);
// $book->tags now contains EXACTLY: sci-fi, favorite
// (any tag not in this list, even ones attached earlier and not
// mentioned here, is removed from the pivot table)

WHY EACH METHOD BEHAVES DIFFERENTLY
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- attach($ids) ADDS the given tag(s) to whatever's already there — it
  does not remove or replace any existing pivot rows, and calling it
  again with an already-attached tag ID can create a duplicate pivot row
  unless the relationship is configured to prevent that.

- detach($id) REMOVES only the specified tag(s) from the book, leaving
  every other currently-attached tag untouched.

- sync($ids) is the most different of the three: it makes the book's tag
  list match EXACTLY the array passed in — any currently-attached tag
  NOT in that array gets detached automatically, and any tag in the array
  not yet attached gets attached. This is why, after step 3 above, classic
  (which was already detached in step 2) and any other previously
  attached tag are guaranteed gone, replaced by exactly [sci-fi, favorite].

WHY THIS WORKS
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- All three methods operate through $book->tags() (calling the
  relationship method, not accessing it as a property) — the trailing
  () is what returns the actual relationship query builder object these
  pivot-management methods live on, as opposed to $book->tags (no
  parentheses), which triggers Eloquent's magic property access and
  returns the already-loaded Collection of Tag models instead.
- Tag::firstOrCreate(['name' => 'sci-fi']) is a convenient Eloquent
  helper that finds an existing row matching the given attributes, or
  creates a new one if none exists — useful here to avoid creating
  duplicate tag rows if this code runs more than once.
- sync() is generally the safest and most predictable of the three for
  representing "this is the complete, current set of tags for this
  book," which is why it's commonly used when handling a form submission
  where a user checked/unchecked a set of tag checkboxes.